A: Hops do, silly! Inside of a hop cone there are sticky yellow resins and oils called lupulin glands’. When boiled, these oils give off different properties including bitterness, flavor compounds and also aromatic qualities. When hops are boiled for 60 minutes, all of the bitterness is extracted. Around 30 minutes, mostly flavor and some bitterness is extracted. With 10 minutes left, mostly aromatic properties are extracted. Brewers also dry hop, meaning they add a dry hop charge post fermentation to increase the aromatic qualities of the beer. There are hundreds of hop varieties, each with different bittering, flavor or aromatic qualities, but it’s mostly the hops added to the beginning of the boil that makes it bitter.